Avoid data races on wxMutexInternal::m_owningThread under Unix

This variable was written to and read from different threads without any
synchronization, which resulted in tons of TSAN warnings -- in addition
to being incorrect, of course.

Fix this by using C++11 atomic type for it if available and just not
doing anything otherwise, as there doesn't seem to be any simple
workaround for this problem without an atomic 64 bit type that our own
wx/atomic.h doesn't currently provide.

src/unix/threadpsx.cpp

@@ -66,6 +66,15 @@
     #include "wx/ffile.h"
 #endif
 
+// We don't provide wxAtomicLong and it doesn't seem really useful to add it
+// now when C++11 is widely available, so just use the standard C++11 type if
+// possible and live without it otherwise.
+#if __cplusplus >= 201103L
+    #include <atomic>
+
+    #define HAS_ATOMIC_ULONG
+#endif // C++11
+
 #define THR_ID_CAST(id)  (reinterpret_cast<void*>(id))
 #define THR_ID(thr)      THR_ID_CAST((thr)->GetId())
 
@@ -187,7 +196,13 @@ private:
     pthread_mutex_t m_mutex;
     bool m_isOk;
     wxMutexType m_type;
-    unsigned long m_owningThread;
+
+    // This member must be atomic as it's written and read from different
+    // threads. If atomic operations are not available, we won't detect mutex
+    // deadlocks at wx level.
+#ifdef HAS_ATOMIC_ULONG
+    std::atomic_ulong m_owningThread;
+#endif
 
     // wxConditionInternal uses our m_mutex
     friend class wxConditionInternal;
@@ -203,7 +218,9 @@ extern "C" int pthread_mutexattr_settype(pthread_mutexattr_t *, int);
 wxMutexInternal::wxMutexInternal(wxMutexType mutexType)
 {
     m_type = mutexType;
+#ifdef HAS_ATOMIC_ULONG
     m_owningThread = 0;
+#endif
 
     int err;
     switch ( mutexType )
@@ -265,11 +282,10 @@ wxMutexInternal::~wxMutexInternal()
 
 wxMutexError wxMutexInternal::Lock()
 {
-    if ((m_type == wxMUTEX_DEFAULT) && (m_owningThread != 0))
-    {
-        if (m_owningThread == wxThread::GetCurrentId())
+#ifdef HAS_ATOMIC_ULONG
+    if ( m_type == wxMUTEX_DEFAULT && m_owningThread == wxThread::GetCurrentId() )
            return wxMUTEX_DEAD_LOCK;
-    }
+#endif // HAS_ATOMIC_ULONG
 
     return HandleLockResult(pthread_mutex_lock(&m_mutex));
 }
@@ -344,8 +360,10 @@ wxMutexError wxMutexInternal::HandleLockResult(int err)
             return wxMUTEX_TIMEOUT;
 
         case 0:
+#ifdef HAS_ATOMIC_ULONG
             if (m_type == wxMUTEX_DEFAULT)
                 m_owningThread = wxThread::GetCurrentId();
+#endif // HAS_ATOMIC_ULONG
             return wxMUTEX_NO_ERROR;
 
         default:
@@ -371,8 +389,10 @@ wxMutexError wxMutexInternal::TryLock()
             break;
 
         case 0:
+#ifdef HAS_ATOMIC_ULONG
             if (m_type == wxMUTEX_DEFAULT)
                 m_owningThread = wxThread::GetCurrentId();
+#endif // HAS_ATOMIC_ULONG
             return wxMUTEX_NO_ERROR;
 
         default:
@@ -384,7 +404,9 @@ wxMutexError wxMutexInternal::TryLock()
 
 wxMutexError wxMutexInternal::Unlock()
 {
+#ifdef HAS_ATOMIC_ULONG
     m_owningThread = 0;
+#endif // HAS_ATOMIC_ULONG
 
     int err = pthread_mutex_unlock(&m_mutex);
     switch ( err )